The present invention relates to an inspection apparatus for inspecting a light transmissive inspection subject such as a light transmissive substrate.
An optical inspection has been often employed to inspect a surface of a light transmissive substrate.
Described below is a related substrate inspection apparatus employing an optical inspection with reference to FIG. 9, which is a schematic view of the related substrate inspection apparatus.
In FIG. 9, light emitted from an illumination lamp 101 to a light transmissive substrate 102 is transmitted through the light transmissive substrate 102 and is taken by an imaging device 103. An image taken by the imaging device 103 may include variations in brightness depending on a state of a surface of the light transmissive substrate 102. Accordingly, the state of the surface of the light transmissive substrate 102 can be found by an inspection of such variations in brightness.
However, such a related substrate inspection apparatus can hardly perform an accurate inspection since the image taken by the imaging device 103 is varied depending on an angle of emission, a level of diffusion, an imaging angle, reflection, and transmission of light emitted from the illumination lamp 101.
In view of the above problem, Japanese Unexamined Patent Publication No. 2006-017487 proposes a method for inspecting a state of a surface of an inspection subject by using light from an illumination lamp diffused by a prism sheet.
FIG. 10 is a schematic view of a substrate inspection apparatus according to Japanese Unexamined Patent Publication No. 2006-017487.
In FIG. 10, a prism sheet 106 is disposed between a lens sheet 104 to be inspected and an illumination lamp 105, the prism sheet 106 having prisms provided on a surface facing the illumination lamp 105. In the substrate inspection apparatus according to Japanese Unexamined Patent Publication No. 2006-017487, light emitted from the illumination lamp 105 is diffused by the prism sheet 106, and the lens sheet 104 is irradiated with the diffused light to have a state thereof taken by an imaging device 107. Thus, the state of a surface of the lens sheet 104 can be inspected while contrasts are emphasized between parts with and without a defect included in the surface (facing the imaging device 107) of the lens sheet 104.
Japanese Unexamined Patent Publication No. 2002-214158 discloses an alternative method that solves the above described problem. Japanese Unexamined Patent Publication No. 2002-214158 proposes a method for inspecting a state of a surface of an inspection subject by irradiating the surface of the inspection subject with illumination light beams simultaneously from two directions substantially perpendicular to and substantially parallel to the surface of the inspection subject (approximately 80 degrees).
FIG. 11 is a schematic view of a substrate inspection apparatus according to Japanese Unexamined Patent Publication No. 2002-214158.
In FIG. 11, there is provided, in addition to an illumination lamp 108, a horizontal illumination lamp 110 that emits light substantially parallel to an inspection subject 109. By irradiating the inspection subject 109 with the light from the horizontal illumination lamp 110, a state of a front surface of the inspection subject 109 can be inspected by an imaging device 111 with less influence by dirt on a rear surface (facing the illumination lamp 108) of the inspection subject 109.
However, there may be a case where there is a scratch on the rear surface (facing the illumination lamp) of the inspection subject and there is an excrescence on the front surface (facing the imaging device) or on the rear surface of the inspection subject. In such a case, the related inspection apparatus has an issue that both the scratch and the excrescence are taken by the imaging device with the contrasts equal to each other. That is, the related inspection apparatus is not capable of distinguishing between the scratch and the excrescence, and therefore, the excrescence adhering to the front or rear surface of the inspection subject cannot be inspected with high accuracy.